1. Field of the Invention
Embodiments of the invention relate to a display device and, more particularly, to a liquid crystal panel and a fabrication method thereof. Although embodiments of the invention are suitable for a wide scope of applications, they are particularly suitable for preventing a defective rubbing and improving productivity of an alignment film process.
2. Description of the Related Art
As consumer interest in information displays grows, the demand for portable information display devices is increasing. Accordingly, research and commercialization of lightweight and thin flat panel displays (“FPD”) have increased. Flat panel displays are replacing the cathode ray tube (“CRT”), which was the most common display device.
The liquid crystal display (“LCD”) device is an FPD device for displaying images that uses the optical anisotropy of liquid crystal molecules. More specifically, the LCD is a display device in which data signals according to image information are individually supplied to liquid crystal cells arranged in a matrix shape to control light transmittance of the liquid crystal cells so as to display desired images. LCD devices exhibit excellent resolution, color rendering and picture quality. Thus, LCD devices are widely being used in notebook computers or desktop monitors, and the like.
FIG. 1 is an exploded perspective view showing the structure of a liquid crystal panel in an LCD device according to the related art. As shown in FIG. 1, the liquid crystal panel includes a color filter substrate 5, an array substrate 10, and a layer of liquid crystal molecules 40 positioned between the color filter substrate 5 and the array substrate 10. The color filter substrate 5 includes a color filter layer C having red (R), green (G) and blue (B) sub-color filters 7, a black matrix 6 for separating the sub-color filters 7 and blocking light transmission, and a transparent common electrode 8 for applying voltage to the layer of liquid crystal molecules 40. The array substrate 10 includes gate lines 16 and data lines 17 that are arranged on the substrate 10 and define pixel regions P. A thin film transistor (TFT), which is a switching element, is formed at respective crossings of the gate lines 16 and the data lines 17, and a pixel electrode 18 is formed in each pixel region P.
The pixel region P is a sub-pixel corresponding to one sub-color filter 7 of the color filter substrate 5, and a color image is obtained by combining light from the three types of red, green and blue sub-color filters 7. In other words, the three red, green and blue sub-pixels form one pixel, and the TFTs are respectively connected to the pixels in the red, green and blue sub-pixels. Alignment films (not shown) for aligning the liquid crystal molecules 40 are respectively formed on the color filter substrate 4 and the array substrate 10.
The process for fabricating a liquid crystal panel can be divided into an array process for forming a driving element on the lower array substrate 10, a color filter process for forming color filters on the upper color filter substrate 4, and a cell process. FIG. 2 is a flow chart illustrating the processes of a method for fabricating the liquid crystal panel in an LCD device according to the related art. The method for fabricating the liquid crystal panel will now be described in detail with reference to FIG. 2.
A plurality of gate lines and a plurality of data lines are formed to define pixel regions on the lower substrate in the array process, and TFTs, driving elements, are formed in the pixel regions and connected with the gate lines and data lines (step S101). Then, pixel electrodes are formed so as to be connected to the TFTs through the array process. The pixels electrodes are used to drive the layer of liquid crystal molecules when a signal is applied through the TFTs.
In a separate process from the array process, R, G and B color filters for implementing colors, and common electrodes are formed on the upper substrate 3 according to the color filter process (step S104).
Subsequently, alignment films are coated on the upper and lower substrates and rubbed to provide an alignment anchoring force or a surface fixing force (namely, a pretilt angle and an alignment direction) to the liquid crystal molecules positioned between the upper and lower substrates (steps S102 and S105). Thereafter, spacers for uniformly maintaining a cell gap are spread on the lower substrate (step S103). Subsequently, a sealant is coated on an outer edge portion of the upper substrate (step S106), and then the lower and upper substrates are attached by applying pressure thereto (step S107).
The lower and upper substrates are formed as large-scale glass substrates. In other words, a plurality of panel regions are formed on a large-scale mother substrate, and the TFTs, the driving elements, and the color filter layers are formed on individual panel regions. To separate the individual panels, the mother substrate is processed (step S108) so as to cut the mother substrate into the individual panels. Thereafter, liquid crystal is injected into each of the processed liquid crystal panels through a liquid crystal injection hole, and the liquid crystal injection hole is encapculated to form the liquid crystal layer (step S109). Then, each liquid crystal panel is inspected to complete fabrication of liquid crystal panels (step S110).
In the alignment film printing and alignment process, the alignment film is patterned and printed on the large-scale mother substrates by using a resin plate having a pattern according to each model of the individual panel region, and then a rubbing process is performed. In the general process of forming the alignment film, the alignment film is patterned and printed corresponding to the plurality of panel regions on the large-scale mother substrate by using the resin plate, but when the size of the mother substrates changes or increases, the resin plate has to be replaced by an appropriately redesigned resin plate. Redesign and fabrication of the replacement resin plate take a long time, so that changing the patterning printing process of the alignment film is difficult and unproductive.
FIG. 3 is an exemplary view showing a phenomenon in that an alignment layer builds-up at an edge portion of an alignment layer pattern. Because the alignment film is pattern-printed, a defect may result from the alignment film printing. More specifically, when the alignment film is pattern-printed, as shown in FIG. 3, the solution builds-up at end portions (namely, the edge portion indicated by a circular dotted line) of the printed pattern 50. The build-up, considerably increases the thickness of the printed pattern 50 at the edge portion compared with the image display region in a central portion of the printed pattern 50. Further, alignment remainders 51 or impurities gather in the build-ups at the end portions of the printed pattern 50. The difference between a thickness (d) of the central portion of the printed pattern 50 and a thickness (P) of the build-ups at the edge portions is sufficient from a step that causes a rubbing scratch and/or a vertical line deficiency during a subsequent rubbing process.